The instant invention relates to boats and more particularly to an alarm system for a boat which is responsive to increased displacement for alerting an owner or attendant of the boat.
In recent years, a significant need has developed for an effective device for alerting an attendant or owner of a boat when an unauthorized boarding of the boat has occurred. In this regard, a large percentage of the md-sized commercial and pleasure boats (between 25 and 65 feet in length) currently in use carry sophisticated and expensive electronic equipment. Because such electronic equipment is often readily removable, the theft of electronic equipment from boats has become a serious problem in recent years. Further, although a wide variety of boat security systems have been heretofore available, most of the previously available security systems have been responsive to entry through hatches, doors, companion ways, etc., rather than boarding. It has been found that security systems which are responsive to entry rather than boarding can often be disarmed before entry takes place, and that in many instances, entry is not required to remove expensive electronic equipment from boats.
While alarm systems which respond to increased displacement of boats have been heretofore available, most of the previously available systems of this type have been less than entirely satisfactory. For example, the system disclosed in the HASELTON U.S. Pat. No. 3,760,396 is adapted so that it is responsive to increased displacement of a boat resulting from unauthorized boarding. However, since this system is adapted to be mounted in the interior bilge area of a boat, it requires the use of through hull piping in the interior bilge area which is in direct open communication with the water beneath the boat. The alarm system disclosed in the BARNES U.S. Pat. No. 4,127,031 is also responsive to increased displacement. However, this system is also adapted to be mounted in the interior bilge area of a boat, and hence it also requires the use of through hull piping to enable it to respond to increased displacement. Other systems which, in addition to the systems disclosed in the aforementioned U.S. Patents to HASELTON and BARNES, represent the closest prior art to the subject invention of which the applicant is aware are disclosed in the CAREY U.S. Pat. No. 2,212,200; HONEYMAN, JR. U.S. Pat. No. 3,101,695; ADAIR U.S. Pat, No. 3,778,804 and SOLTESZ U.S. Pat. No. 4,058,792. However, since none of these systems incorporate a sensor which is mounted on an exterior hull surface of a boat beneath the waterline for sensing increased displacement, they are believed to be of only general interest with respect to the subject invention.
The instant invention provides an effective alarm system which is responsive to increased water pressure on an exterior hull surface of a boat for sensing increased displacement, such as caused by unauthorized boarding or by taking on water. In particular, the alarm system of the subject invention comprises a housing which is adapted to be secured to an exterior hull surface of a boat below the waterline thereof. The housing has an open cylinder formed therein, and the alarm system further comprises a displaceable piston which is received in the cylinder and cooperates therewith to define an air-tight compressible chamber on the exterior of the boat. The piston is received in the cylinder so that it is responsive to water pressure on the exterior of the boat hull for movement between a nondisplaced position wherein the chamber has a first volume and a displaced position wherein the chamber has a reduced second volume. The alarm system further comprises means for resiliently resisting movement of the displaceable piston from the nondisplaced position thereof towards the displaced position thereof and signalling means responsive to movement of the piston from the nondisplaced position thereof to the displaced position thereof for alerting an attendant or owner of the boat. The means for resiliently resisting movement of the piston preferably comprises means for supplying a compressed gas to the chamber in order to resiliently resist movement of the piston toward the displaced position thereof, and more preferably the means for resiliently resisting movement comprises an air compressor for supplying compressed air to the chamber in order to resiliently resist movement of the piston toward the displaced position thereof. The signalling means preferably comprises a fixed contact mounted in a fixed position in the chamber and a movable contact which is movable with the piston toward the displaced position thereof for making electrical contact with the fixed contact. The signalling means preferably comprises a signalling unit which is actuatable in response to electrical contact between the fixed and movable contacts for signalling an attendant or owner of the boat. The device preferably still further comprises switch means for actuating the air compressor to initially move the piston from the displaced position thereof to the nondisplaced position thereof and for thereafter actuating the signalling unit so it is operative in response to electrical contact between the fixed and movable contacts for signalling an owner or attendant of the boat.
It has been found that the device of the instant invention can be effectively utilized for alerting an attendant or owner that the displacement of a boat has been increased, as a result of unauthorized boarding by an intruder, by taking on water, etc. Specifically, it has been found that by mounting the housing and the displaceable piston of the device of the instant invention on an exterior hull surface of a boat below the waterline thereof, the device is extremely sensitive and highly responsive to increased displacement of the boat. However, because it is mounted on an exterior hull surface of the boat, the device does not require through hull piping which introduces water into the interior bilge areas of the boat. It has been further found that by first actuating the compressor to move the displaceable piston from the displaced position thereof to the nondisplaced position thereof and by immediately thereafter deactuating the compressor, the alarm system can effectively compensate for normal changes in the displacement of a vessel, such as caused by variations in the amounts of fuel and/or drinking water on board the vessel. However, once actuated, the system is responsive to increased displacement of the vessel by sensing the increased pressure applied to the exterior surfaces of the displaceable piston. As a result, the alarm system of the subject invention is able to effectively respond to changes in the displacement of the vessel so that an attendant or owner can be alerted.
Accordingly, it is an object of the instant invention to provide an effective alarm system for alerting an attendant or owner of a boat that the displacement of the boat has increased.
Another object of the instant invention is to provide an effective alarm system for a boat which is responsive to boarding by an unauthorized intruder.
A still further object of the instant invention is to provide an alarm system including a sensor portion which is adapted to be mounted on an exterior hull surface of a boat for sensing increased displacement.
Other objects, features and advantages of the invention shall become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawings.